Figure 3.
Qualitative representation of the Oldroyd-B fluid. The deviatoric stress is given by the sum of the Newtonian stress of the solvent (viscosity ηs) and the viscoelastic stress of the upper convected Maxwell fluid. The latter is characterized by a polymer viscosity ηp and an elastic modulus μ. The ratio of ηp/μ gives the polymer relaxation time λ. Note that the spring-dashpot analogy is not to be taken quantitatively, certainly not at large deformations where one encounters strongly nonlinear responses.